Let number of pounds of black olive = x
Let number of pounds of green olive = y
Then total number of olive will be (x+y)
Given that she buys 4 pounds of olives. so we get equation
x+y=4
or x=4-y...(i)
Given that cost of 1 pound of black olive = $3
then cost of x pounds of black olive = 3x
Given that cost of 1 pound of green olive = $5
then cost of y pounds of green olive = 5y
which gives total cost = (3x+5y)
Given that "she spends $15.50" so we get equation:
3x+5y=15.50...(ii)
Now we just need to solve both equations.
Plug value of x from equation (i) into (ii)
3x+5y=15.50
3(4-y)+5y=15.50
12-3y+5y=15.50
12+2y=15.50
2y=15.50-12
2y=3.5
y=3.5/2
y=1.75
Now plug value of y into (i)
x=4-y=4-1.75=2.25
Hence final answer is given by:
system of equation is x=4-y, 3x+5y=15.50
Number of pounds of black olive = 2.25 pound
Number of pounds of green olive = 1.75 pound